This invention relates to an ink jet printing method using an anthrapyridone dye mixture as a colorant in an ink jet ink composition.
Ink jet printing is a non-impact method for producing images by the deposition of ink droplets in a pixel-by-pixel manner to an image-recording element in response to digital signals. There are various methods which may be utilized to control the deposition of ink droplets on the image-recording element to yield the desired image. In one process, known as continuous ink jet, a continuous stream of droplets is charged and deflected in an imagewise manner onto the surface of the image-recording element, while unimaged droplets are caught and returned to an ink sump. In another process, known as drop-on-demand ink jet, individual ink droplets are projected as needed onto the image-recording element to form the desired image. Common methods of controlling the projection of ink droplets in drop-on-demand printing include piezoelectric transducers and thermal bubble formation. Ink jet printers have found broad applications across markets ranging from industrial labeling to short run printing to desktop document and pictorial imaging.
The inks used in the various ink jet printers can be classified as either dye-based or pigment-based. A dye is a colorant, which is dissolved in the carrier medium. A pigment is a colorant that is insoluble in the carrier medium, but is dispersed or suspended in the form of small particles, often stabilized against flocculation and settling by the use of dispersing agents. The carrier medium can be a liquid or a solid at room temperature in both cases. Commonly used carrier media include water, mixtures of water and organic co-solvents and high boiling organic solvents, such as hydrocarbons, esters, ketones, etc.
The choice of a colorant in ink jet systems is critical to image quality. For colors such as cyan, magenta, yellow, green, orange, etc., the peak wavelength (xcex-max), the width of the absorption curve and the absence of secondary absorptions are important. The colorant should also have a high degree of light fastness after printing onto the ink-receiving element. For aqueous dye-based inks, the dye needs to be sufficiently soluble in water to prepare a solution that is capable of producing adequate density on the receiving element and stable for extended periods of storage without precipitation. High quality photorealistic ink jet printing with dye-based inks requires dyes which will provide both bright hue and good light stability. It is difficult to find dyes, particularly magenta dyes, which meet all of these requirements.
Aqueous dye-based inks for high quality photorealistic ink jet printing require water-soluble dyes with excellent color and high light and water fastness. Typically the dyes are chosen from acid, direct and reactive dyestuffs developed for the dyeing of natural fibers such as paper, wool and cotton. Water solubility of these dyes is due to the incorporation of negatively charged substituent groups such as sulfo or carboxy.
It is well known in the art of color measurement that hue and brightness are among the basic perceptual attributes of color. (For a complete description of color measurement refer to xe2x80x9cMeasuring Colorxe2x80x9d, 2nd Edition by R. W. G Hunt, published by Ellis Horwood Ltd., 1991.) Hue is defined as the attribute of a visual sensation according to which an area appears to be similar to one, or to proportions of two, of the perceived colors red, yellow, green and blue. In terms of the CIELAB color space, hue is mathematically defined by hue angle, hxc2x0, according to
hxc2x0=tanxe2x88x921(b*/a*)xe2x80x83xe2x80x83Equation 1
where a* is a measure of how green or red the color is and b* is a measure of how blue or yellow a color is. Brightness is defined as the attribute of a visual sensation according to which an area appears to exhibit more or less light. In terms of the CIELAB color space, brightness is mathematically defined by chroma, C*, according to
C*=(a*2+b*2)xc2xdxe2x80x83xe2x80x83Equation 2
For the production of high quality photorealistic images via ink jet printing, ink sets must be able to provide printed images having good color characteristics. In particular, it is desirable to have hue angles of about 270 for the blue record and about 339 for the magenta record. It is also desirable to maximize chroma (also referred to as vividness), particularly for the red record.
U.S. Pat. No. 6,152,969; EP 1,063,268; EP 1,067,155; WO 00/23440; WO 01/18123; JP 2000-256587 and JP 2001-072884 describe magenta anthrapyridone dyes for ink jet printing. However, there is a problem with these dyes in that when they are printed with typical yellow dyes, the chroma values of the resulting red records are too low.
It is an object of this invention to provide an ink jet printing method using magenta inks that give good hue when printed. It is another object of this invention to provide an ink jet printing method using magenta inks that, when printed with typical yellow inks, give high chroma values for the resulting red records. It is another object of this invention to provide an ink jet printing method using magenta inks with good fastness to light when printed.
These and other objects are achieved in accordance with this invention which relates to an ink jet printing method, comprising the steps of
A) providing an ink jet printer that is responsive to digital data signals;
B) loading the printer with an ink-receiving element comprising a support having thereon an ink-receiving layer;
C) loading the printer with an ink jet ink composition comprising water, a humectant and a mixture of a water-soluble, magenta anthrapyridone dye and Reactive Red 23, Reactive Red 24, Reactive Red 31, Reactive Red 120, Reactive Red 180, Reactive Red 241, Acid Red 35, Acid Red 52, Acid Red 249, Acid Red 289, Acid Red 388, Direct Red 227 or CAS No. 153204-88-7; and
D) printing on the ink-receiving layer using the ink jet ink in response to the digital data signals.